Display device substrate, method for manufacturing the display device substrate, liquid-crystal device, and electronic equipment

ABSTRACT

A panel substrate includes a substrate, a plurality of display electrodes running in parallel on the substrate, and a plurality of wirings respectively continuous from the display electrodes formed on the substrate. The display electrodes and the wirings respectively have a bilayer structure of a transparent conductive layer and a metal layer. The metal layer of the display electrode is substantially narrower in width than the width of the transparent conductive layer.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application of U.S. Ser. No. 09/785,511 filed Feb.16, 2001 now U.S. Pat. No. 6,850,307.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a display device substrate for use in adisplay device, a manufacturing method for manufacturing the displaydevice substrate, a liquid-crystal display device incorporating thedisplay device substrate, and electronic equipment incorporating theliquid-crystal device.

2. Description of the Related Art

Passive-matrix liquid-crystal devices include two panel substrates, eachof which has a plurality of display electrodes running in parallel andwirings electrically connected to the respective display electrodes forapplying the display electrodes with voltages. The two panel substratesare assembled to be opposed to each other in a manner such that the twopanel substrates form a grating.

Active-matrix liquid-crystal devices having a thin-film diode (TFD)connected to each pixel are constructed by assembling a pair ofsubstrates, i.e., an element substrate, and a counter substrate, in themutually opposing position thereof. The TFDs, wirings respectivelyconnected to the TFDs, and pixel electrodes serving as displayelectrodes are arranged on the element substrate. Arranged on thecounter substrate is a plurality of display electrodes running inparallel, and wirings electrically connected to the respective displayelectrodes for applying the display electrodes with voltages. Theelement substrate and the counter substrate are assembled together insuch a manner that the pixel electrodes on the element substrate areopposed in alignment to the display electrodes on the counter substrate.

As the definition of display becomes high, and the outline areasurrounding a display area becomes narrow in these conventionalliquid-crystal devices, the wirings respectively connected to thedisplay electrodes become fine. As such a fine line design is currentlyintroduced, the resistance of the wiring increases. A drop in thevoltage applied from a drive circuit through the wiring is notnegligible.

The passive-matrix liquid-crystal devices typically employ an STN (SuperTwisted Nematic) liquid crystal. The display of such liquid-crystaldisplay device is susceptible to a subtle variation in the drivevoltage. The wiring is electrically connected to the display electrodeand is physically continuous from the display electrode, and isfabricated of a transparent conductive film for use as the displayelectrode, such as an ITO (Indium Tin Oxide) film. The wiring isproduced at the same time when the display electrodes are produced. As aresult, the display electrode and the wiring thereof are fabricated ofthe transparent conductive film having substantially the same filmthickness.

The wiring has a finer line width to meet compact design requirement. Toreduce resistance in the wiring, an increase in the thickness of thetransparent conductive film is contemplated. However, as the thicknessof the wiring increases, the time required to form the film lengthens.As the wiring increases in thickness, the display electrode, which isconcurrently produced, also increases in thickness. This leads to areduction in the transmittance ratio of the display electrode.

In view of the above problem, the present invention has been developed.The present invention is thus designed to achieve at least one of thethree objects of reducing electrical resistance in the wiring,increasing the light transmittance ratio of the display electrode, andshortening the time required to form the display electrode and thewiring.

SUMMARY OF THE INVENTION

A display device substrate includes a plurality of display electrodes,and a plurality of wirings for supplying the plurality of displayelectrodes with a voltage, wherein the plurality of wirings includes alaminated structure composed of a transparent conductive layer formed ofthe same layer as that of the display electrodes, and a metal layerfabricated of a metal having an electrical resistance lower than that ofthe transparent conductive layer.

Since the display device substrate thus constructed has the wiringsfabricated of the laminated structure of the transparent conductivelayer and the metal layer, the resistance of the wirings is low comparedwith the case in which the wiring is fabricated of the transparentconductive layer only. The liquid-crystal display device having thedisplay device substrate of this invention suffers less from imagequality degradation attributed to a voltage drop in the wirings.

Since this arrangement eliminates the need for thickening thetransparent conductive layer for the purpose of reducing the electricalresistance of the wirings, the film thickness of the transparentconductive layer in the display electrode, which is produced typicallyconcurrently with the transparent conductive layer in the wiring, is notexcessively increased. The light transmittance ratio of the displayelectrode becomes higher compared with the case in which the electricalresistance of the wirings is reduced only by thickening the transparentconductive layer.

The transparent conductive layers used in the display electrodes and thewirings become thin, compared with the case in which the electricalresistance of the wirings is reduced only by thickening the transparentconductive layer. The time required to form the display device substrateis thus shortened.

(2) In the display device substrate discussed in paragraph (1), thedisplay electrode may include a laminated structure composed of atransparent conductive layer, and a metal layer fabricated of a metalhaving an electrical resistance lower than that of the transparentconductive layer.

Since the display electrode has the laminated structure formed of thetransparent conductive layer and the metal layer, the electricalresistance of the display electrode becomes lower compared with the casein which the display electrode is fabricated of the transparentconductive layer only. Since lowering the electrical resistance of thedisplay electrode does not involve increasing the thickness of thetransparent conductive layer, the light transmittance ratio of thedisplay electrode is increased.

(3) In the display device substrate discussed in paragraph (2), themetal layer in the display electrode is preferably narrower in widththan the transparent conductive layer. With this arrangement, theelectrical resistance of the display electrode is lowered with almost nodrop caused in the brightness level of the display.

(4) In the display device substrate discussed in paragraph (1) or (2),the display electrode preferably includes the laminated structure of thetransparent conductive layer and the metal layer, and wherein the metallayer has an aperture partially opened in the laminated structure.

If the display device substrate of the above arrangement is used as arear substrate of the pair of the substrates forming the liquid-crystaldevice, the aperture of the display electrode permits light to passtherethrough while the metal layer in the display electrode reflectslight therefrom. A transflective liquid-crystal device thus results.Since the display electrode fabricated of the transparent conductivelayer is present in the aperture of the metal layer, electric fieldapplied to the liquid crystal in an area corresponding to the apertureis not disturbed.

(5) In the display device substrate discussed in paragraphs (1) through(4), the wirings may be routed from the ends of the respective displayelectrodes in the peripheral portion of the display device substrate.Since a wiring is typically routed in a frame outline area of asubstrate, its length becomes long. The wirings, formed of the laminatedstructure of the transparent conductive layer and the metal layer inthis invention, are particularly advantageous in lowering wiringresistance.

(6) The liquid-crystal display device of the present invention relatesto the one which encapsulates a liquid crystal between a pair ofsubstrates, and includes the display device substrate discussed inparagraph (1) through (5) as at least one of the pair of substrates. Inthe liquid-crystal display device thus constructed, the wirings have thelaminated structure of the transparent conductive layer and the metallayer, the electrical resistance of the wirings is rendered lower thanwhen the wirings are formed of the transparent conductive layer only.The liquid-crystal display device having the display device substrate ofthis invention suffers less from image quality degradation attributed toa voltage drop in the wirings.

Since this arrangement eliminates the need for thickening thetransparent conductive layer for the purpose of reducing the electricalresistance of the wirings, the film thickness of the transparentconductive layer in the display electrode, which is produced typicallyconcurrently with the transparent conductive layer for the wiring, isnot excessively increased. The light transmittance ratio of the displayelectrode becomes higher compared with the case in which electricalresistance of the wirings is reduced only by thickening the transparentconductive layer.

The transparent conductive layers of the display electrode and thewirings become thinner compared with the case in which the electricalresistance of the wirings is reduced only by thickening the transparentconductive layer. The time required to form the display device substrateis thus shortened.

(7) The liquid-crystal display device of the present invention, includesthe display device substrate discussed in paragraph (4), a countersubstrate opposed to the display device substrate, and a liquid-crystallayer encapsulated between the display device substrate and the countersubstrate, wherein the liquid-crystal device has a transmissive-typedisplay function using the aperture of the metal layer as a lighttransmissive section and a reflective-type display function using theregion of the metal layer as a light reflective section.

Since in the liquid-crystal device thus constructed, the wirings havethe laminated structure of the transparent conductive layer and themetal layer, the electrical resistance of the wirings is rendered lowcompared with the case in which the wirings are formed of thetransparent conductive layer only. The liquid-crystal display devicehaving the display device substrate of this invention suffers less fromimage quality degradation due to a voltage drop in the wirings.

Since this arrangement eliminates the need for thickening thetransparent conductive film for the purpose of reducing the electricalresistance of the wirings, the film thickness of the transparentconductive layer in the display electrode, which is produced typicallyconcurrently with the transparent conductive layer in the wiring, is notexcessively increased. The light transmittance ratio of the displayelectrode becomes high, compared with the case in which the electricalresistance of the wirings is reduced only by thickening the transparentconductive layer.

The transparent conductive layers of the display electrode and thewirings become thin, compared with the case in which electricalresistance of the wirings is reduced only by thickening the transparentconductive layer. The time required to form the transparent conductivelayer is thus shortened.

(8) Electronic equipment of the present invention includes theliquid-crystal device discussed in paragraph (6) or (7) as a displaymeans. The electronic equipment provides the above-discussed advantagesof the display device. Electronic equipment having display means of ahigh image quality is provided.

(9) A manufacturing method of the present invention for manufacturingthe display device substrate discussed in one of paragraphs (1) through(5), includes a transparent conductive layer fabrication step forfabricating a transparent conductive layer on the display devicesubstrate, a metal layer depositing step for depositing a metal layer onthe transparent conductive layer, and an etching step for concurrentlyetching the transparent conductive layer and the metal layer.

In accordance with the manufacturing method, the transparent conductivelayer and the metal layer are laminated, and the laminated structure isthen patterned by a single etching process to form a wiring.

(10) A manufacturing method of the present invention for manufacturingthe display device substrate discussed in one of paragraphs (1) through(5) includes a transparent conductive layer fabrication step forfabricating a transparent conductive layer on the display devicesubstrate, a metal layer depositing step for depositing a metal layer onthe transparent conductive layer, a first etching step for concurrentlyetching the transparent conductive layer and the metal layer using afirst photoresist film, and a second etching step for etching the metallayer only using a second photoresist film, wherein the secondphotoresist film having a predetermined pattern is created by subjectingthe first photoresist film to exposure and development processes.

In accordance with this manufacturing method, the second etching stepuses the second photoresist film that is obtained by subjecting thefirst photoresist film, having a predetermined pattern and used in thefirst etching step, to the exposure and development processes. Throughthe second etching step, the metal layer becoming a display electrode isetched away with part thereof being left. The photoresist is thenremoved. The pattern of the display electrode and the wirings is thusformed of a portion where both the transparent conductive layer and themetal layer are laminated and a portion where the transparent conductivelayer only is present.

In accordance with the manufacturing method, the application and thenthe removal of the photoresist film are respectively performed only onetime, resulting in a pattern where the metal layer and the transparentconductive layer are laminated. This manufacturing method results in asubstantial decrease in manufacturing steps in comparison to aconventional manufacturing method in which the transparent conductivelayer and the metal layer are separately patterned. In the conventionalmanufacturing method, each of the application and removal of thephotoresist twice must respectively be performed twice. The transparentconductive layer and the metal layer are laminated, and the resultinglaminated structure is subjected to a single etching step for patterningto produce the wiring.

(11) In a manufacturing method for manufacturing a display devicesubstrate discussed in paragraph (10), the metal layer in the displayelectrode may be etched through the second etching step so that themetal layer is left on only the edge portion of the transparentconductive layer. In accordance with this manufacturing method, thedisplay electrode having a low electrical resistance is patterned withsubstantially reduced number of steps with almost no drop involved inthe brightness level of the display.

(12) In the manufacturing method for manufacturing a display devicesubstrate discussed in paragraph (10), the metal layer in the displayelectrode may be etched through the second etching step so that themetal layer has an aperture on the transparent conductive layer. Inaccordance with the manufacturing method, the display device substratehaving the advantages discussed in paragraph (4) is produced with asmaller number of manufacturing steps involved.

(13) A liquid-crystal device of the present invention includes a pair ofdisplay device substrates, and a liquid crystal encapsulated between thedisplay device substrates, wherein one of the pair of display devicesubstrates includes a plurality of pixel electrodes, and a plurality oftwo-terminal-type switching elements, each connected to the respectivepixel electrode, the other of the pair of display device substratesincludes a plurality of display electrodes arranged in stripes to beopposed to the plurality of pixel electrodes, and wirings respectivelyconnected to the display electrodes, the plurality of display electrodesincludes a transparent conductive layer, and the wirings include atransparent conductive layer formed of the same layer as that of thedisplay electrodes, and a metal layer fabricated of a metal having anelectrical resistance lower than that of the transparent conductivelayer. The two-terminal switching element here may be a TFD (Thin FilmDiode).

(14) A liquid-crystal device of the present invention includes a pair ofdisplay substrates, and a liquid crystal encapsulated between thedisplay device substrates, wherein one of the pair of display devicesubstrates includes a plurality of pixel electrodes, and a plurality ofthree-terminal-type switching elements, each connected to the respectivepixel electrode, the other of the pair of display device substratesincludes a plurality of display electrodes arranged in stripes to beopposed to the plurality of pixel electrodes, and wirings respectivelyconnected to the display electrodes, the plurality of display electrodesincludes a transparent conductive layer, and the wirings include atransparent conductive layer formed of the same layer as that of thedisplay electrodes, and a metal layer fabricated of a metal having anelectrical resistance lower than that of the transparent conductivelayer. The three-terminal switching element may be a TFT (Thin-FilmTransistor).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing one embodiment of theliquid-crystal device of the present invention.

FIG. 2 is an exploded cross-sectional view showing the construction ofthe liquid-crystal device of FIG. 1.

FIG. 3 is a plan view showing one of panel substrates forming theliquid-crystal device of FIG. 1.

FIG. 4 is a plan view showing the other panel substrate forming theliquid-crystal device of FIG. 1.

FIG. 5 is a plan view showing, in enlargement, a single displayelectrode and a wiring of the panel substrate of FIG. 4.

FIG. 6(A) is a cross-sectional view showing the wiring taken along lineF—F in FIG. 5, and FIG. 6(B) is a cross-sectional view showing thedisplay electrode taken along line G—G in FIG. 5.

FIGS. 7(A)-7(E) are cross-sectional views partially showing the panelsubstrate in the manufacturing process of the panel substrates.

FIGS. 8(A)-8(C) show embodiments of the electronic equipment of thepresent invention, wherein FIG. 8(A) shows a mobile telephone, FIG. 8(B)shows a wristwatch, and FIG. 8(C) shows a mobile information terminal.

FIG. 9 is a plan view showing a modification of the single displayelectrode and its associated wiring of the panel substrate shown in FIG.4.

FIG. 10 is a cross-sectional view showing the display electrode takenalong line G—G in FIG. 9.

FIG. 11 is a block diagram showing an electrical control system of theelectronic equipment.

FIG. 12 is an exploded perspective view showing a major portion ofanother embodiment of the liquid-crystal device of the presentinvention.

FIG. 13 is a cross-sectional view showing a major portion of theliquid-crystal device in FIG. 12.

FIG. 14 is a perspective view showing a single TFD used in theliquid-crystal device of FIG. 12.

FIG. 15 is a perspective view showing the external appearance of theliquid-crystal device of FIG. 12.

FIG. 16 is a plan view showing one of display device substrates formingthe liquid-crystal device of FIG. 12.

FIG. 17 is a circuit diagram showing a circuit arrangement of yetanother embodiment of the liquid-crystal device of the presentinvention.

FIG. 18 is a cross-sectional view showing a major portion of theliquid-crystal device of FIG. 17.

FIG. 19 is a plan view showing the external appearance of theliquid-crystal device of FIG. 17.

FIG. 20 is a drive voltage waveform diagram showing a 1H bias voltageswing drive method as a drive method for the liquid-crystal device ofFIG. 17.

FIG. 21 is a drive voltage waveform diagram showing a field polarityreversal drive method which is a typical drive method for use inactive-matrix TFT liquid-crystal devices.

FIG. 22 is a graph plotting measurement results for verifying therelationship between a shift amount of a threshold voltage and operatingtime.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention are specificallydiscussed, referring to the drawings.

FIG. 1 is an exploded perspective view diagrammatically showing aliquid-crystal device 10 as a display device of the present invention.FIG. 2 is a cross-sectional view diagrammatically showing theliquid-crystal device 10 of FIG. 1. As shown, the liquid-crystal device10 includes a liquid-crystal panel 14 as a display panel, and abacklight unit 40 having a light guide plate 44 arranged behind theliquid-crystal panel 14. The liquid-crystal device 10 also includes abracket member (not shown) for protecting and keeping the liquid-crystalpanel 14 and the backlight unit 40 in position.

Referring to FIG. 2, the liquid-crystal panel 14 is constructed byarranging a first panel substrate 20 and a second panel substrate 30 inan opposing position. Spacers (not shown) are dispersed between thefirst panel substrate 20 and the second panel substrate 30 to keep thetwo substrates apart by a predetermined gap therebetween. The firstpanel substrate 20 is a display device substrate that is produced byforming striped display electrodes 22 on one side of a substrate 21fabricated of a transparent material such as glass or synthetic resin.

The second panel substrate 30 works as a display device substrate thatis produced by forming striped display electrodes 32 on one side of asubstrate 31 fabricated of a transparent material such as glass orsynthetic resin. The display electrodes 22 of the first panel substrate20 and the display electrodes 32 of the second panel substrate 30 arearranged to be opposed to each other in a manner such that a gratingconfiguration is formed. A so-called passive-matrix liquid-crystal panelresults.

A sealing member 19 is inserted between the pair of substrates 20 and 30in the peripheral outline thereof in a substantially rectangularconfiguration when viewed from an arrow A as shown in FIG. 2. The twopanel substrates 20 and 30 are glued onto each other with the sealingmember 19. Conductive members 26 of particles are included in thesealing member 19, thereby electrically connecting wirings 36 on thesecond panel substrate 30 to wirings 24 leading to the displayelectrodes 22 on the first panel substrate 20 via the conductive members26. In this way, voltages input to terminals 39 are applied to thedisplay electrodes 22.

A liquid crystal, for example, a liquid crystal 18 of an STN type, isintroduced into the gap between the first panel substrate 20 and thesecond panel substrate 30 and enclosed by the sealing member 19, througha liquid crystal injection port (not shown) arranged in the sealingmember 19. The liquid-crystal injection port is then closed by a sealmaterial (now shown) after a liquid-crystal injection process.

A first polarizer 16 is mounted on the external side of the first panelsubstrate 20, while the second polarizer 17 is mounted on the externalside of the second panel substrate 30. A retardation film 12 is arrangedbetween the first polarizer 16 and the first panel substrate 20.Alternatively, a retardation film 12 may be arranged between the secondpolarizer 17 and the second panel substrate 30. It is also acceptablethat retardation films 12 are respectively arranged external to both thefirst panel substrate 20 and the second panel substrate 30.

The liquid-crystal panel 14 is provided with a plurality of terminals 39on an overextension 38 of the second panel substrate 30 extending overfrom the edge of the first panel substrate 20. Connected to theterminals 39 are terminals of wiring boards 64 shown in FIG. 1, such asflexible boards. The wiring boards 64 bear drive ICs (not shown) fordriving the display electrodes 22 and 32 (see FIG. 2) on theliquid-crystal panel 14. The terminals of the wiring boards 64 connectedto the output terminals of the drive ICs are respectively connected theterminals 39 formed on the second panel substrate 30, thereby feedingdrive voltages to the display electrodes 22 and 23.

In the liquid-crystal panel 14, the liquid crystal 18 is applied with avoltage difference between signals supplied to each of the plurality ofdisplay electrodes 22 formed on the first panel substrate 20 andsupplied to each of the plurality of display electrodes 32 formed on thesecond panel substrate 30. The alignment of liquid-crystal molecules isthus controlled to turn on or turn off displaying.

Alternatively, the first panel substrate 20 or the second panelsubstrate 30 may be provided with a mount area for accommodating thedrive ICs. The drive ICs are thus mounted on the first panel substrate20 or the second panel substrate 30 using the COG (Chip On Glass)technology. In this case, the signals and voltages are supplied to thedrive ICs on the panel substrate through flexible boards.

Referring to FIG. 2, the pair of panel substrates 20 and 30 are shownwidely separated for clarifying the details. In practice, the pair ofpanels 20 and 30 are spaced by a small gap as narrow as several μm todozens of μm. Referring to FIG. 20, the first polarizer 16 and theretardation film 12 are shown separated from the first panel substrate20, and the second polarizer 17 is shown separated from the second panelsubstrate 30. In practice, however, the retardation film 12 is almost incontact with the first panel substrate 20, the second polarizer 17 isalmost in contact with the second panel substrate 30, and the firstpolarizer 16 is almost in contact with the retardation film 12. Althoughseveral striped display electrodes 22 and 23 are shown, there areemployed a large number of striped electrodes, the number of which isdependent on the resolution requirement of the matrix display inpractice.

Referring to FIG. 1, the backlight unit 40 includes a fluorescent tube50 as a light source, the light guide plate 44, a lens sheet 42 as alight diffusing plate, a backlight support bracket 56, and a reflector60. The fluorescent tube 50 is connected to an output terminal of aninverter (not shown) through a connector assembly 51. The invertersupplies the fluorescent tube 50 with a predetermined voltage.

The light guide plate 44 is fabricated of a transparent synthetic resin,for example. The fluorescent tube 50 as a light source is placedsubstantially in contact with an end face 45 of the light guide plate44. Light from the fluorescent tube 50 enters through the end face 45into and travels the light guide plate 44, and exits from the light exitsurface of the light guide plate 44 facing the liquid-crystal panel 14.The light then illuminates the entire display area of the liquid-crystalpanel 14. The light guide plate 44 has a flat surface area substantiallycoextending with the flat surface of the liquid-crystal panel 14 exceptfor the overextension 38 of the liquid-crystal panel 14.

The light guide plate 44 is tapered from the thickest portion thereof atthe fluorescent tube 50 to be gradually thinner at it goes away in awedge-like cross section. With the light guide plate 44 configured inthis way, the quantity of light radiated toward the liquid-crystal panel14 from the light guide plate 44 is made uniform, for example, with nodifference in light intensity between at a point in the vicinity of thefluorescent tube 50 and the farthest point away from the fluorescenttube 50.

The lens sheet 42, arranged in front of the light guide plate 44,diffuses light emitted from the light guide plate 44, therebyilluminating the entire display area of the liquid-crystal panel 14 withuniform light. The reflector 60 surrounds the fluorescent tube 50 exceptthe side thereof facing the light guide plate 44 so that light from thefluorescent tube 50 is reflected toward the light guide plate 44.Referring to FIG. 1, the fluorescent tube 50, shown external to thereflector 60, is actually housed in the reflector 60.

The fluorescent tube 50 of the backlight unit 40 is supplied with powerfrom the unshown inverter. In response to a direct-current voltage of 5V, the inverter outputs a 250 V, 100 kHz alternating-current voltage tothe fluorescent tube 50. Instead of the fluorescent tube 50, an LED maybe used as a light source. The LED may be arranged alongside the lightguide plate 44.

The backlight support bracket 56, having a bottom portion 57, supportsthe backlight unit 40 from the backside thereof. The backlight supportbracket 56 also has a plurality of guide portions 58 verticallyextending from the bottom portion 57 thereof for aligning the backlightunit 40. The guide portions 58 are respectively shaped to receive theend faces 46 and 47 of the light guide plate 44, and are in abutmentwith the end faces 46 and 47 of the light guide plate 44. In this way,the light guide plate 44 is in substantially parallel alignment with thesurface of the bottom portion 57.

Except for the side facing the fluorescent tube 50, the backlightsupport bracket 56 has the guide portions 58 that have planar surfacessubstantially in contact with the end faces 46 and 47 of the light guideplate 44. Since the guide portions 58 and the bottom portion 57 of thebacklight support bracket 56, facing the light guide plate 44, have asufficiently high light reflectance, light from the fluorescent tube 50is reflected therefrom at a high efficiency. The backlight supportbracket 56 is integrally formed with the reflector 60.

FIG. 3 is a plan view diagrammatically showing the first panel substrate20 viewed from the front of the panel and seen through the displayelectrodes 22, etc. FIG. 4 is a plan view diagrammatically showing thesecond panel substrate 30 vied from the front. With the liquid-crystalpanel 14 viewed from the display screen side as shown in FIG. 1, thesecond panel substrate 30 shown in FIG. 4 is laminated behind the firstpanel substrate 20 shown in FIG. 3. In the laminated state thereof, theoverextension 38 of the second panel substrate 30 outwardly overextendsover from the first panel substrate 20. The cross-sectional view of theliquid crystal shown in FIG. 2 is taken along line S—S shown in FIG. 3and FIG. 4.

Referring to FIG. 3, the first panel substrate 20 includes the displayelectrodes 22 formed as a predetermined pattern on the substrate 21, andthe wirings 24 to which the display electrodes 22 respectively lead. Thedisplay electrodes 22 function as scanning electrodes or signalelectrodes. The ends of the wirings 24 are formed as pads 25 serving asterminals to be connected to the conductive members 26 (see FIG. 2).

Referring to FIG. 4, the second panel substrate 30 includes the displayelectrodes 32, the wirings 34, and the wirings 36. The plurality ofdisplay electrodes 32 run in parallel in a predetermined pattern on thesubstrate 31. The display electrodes 32 function as the others of thescanning electrodes and the signal electrodes. The wirings 34 arecontinuous from the respective display electrodes 32, and are routedalong the peripheral portion of the substrate 31. The wirings 34 runtoward the overextension 38 of the second panel substrate 30 and areterminated at the terminals 39 there. The overextension 38 outwardlyextends over from the opposed first panel substrate 20 in a plan view.

The ends 37 of the wirings 36 are formed in pads that serve asconnection terminals to be connected to the conductive members 26. Theconductive members 26 electrically respectively connect the pads 37 tothe pads 25 as the connection terminals at the ends of the wirings 24formed on the first panel substrate 20. The conductive members 26 areconductive particles mixed into the sealing member 19 as shown in FIG.2. The wirings 36 also extend into the overextension 38, thereby formingthe terminals 39 at the other ends thereof.

The terminals 39 are formed as parts of the wirings 34 and 36, and areelectrically connected to the corresponding display electrodes 22 and32. The display electrodes 22 on the first panel substrate 20 areconnected to the corresponding terminals 39 via the wirings 24 formed onthe first panel substrate 20, the conductive members 26, and the wirings36 formed on the second panel substrate 30.

Referring to FIG. 3, the display electrodes 22 on the substrate 21 arecoated with an alignment layer (not shown), fabricated of polyimide, forexample. The alignment layer is then subjected to a rubbing process in apredetermined direction. Referring to FIG. 4, the display electrodes 32on the substrate 31 are coated with an alignment layer (not show)fabricated of polyimide, for example. The alignment layer is subjectedto a rubbing process in a predetermined direction.

FIG. 5 is an enlarged plan view diagrammatically showing a singledisplay electrode 32 on the second panel substrate 30 and a wring 34extending continuously from the display electrode 32. FIG. 6(A) is adiagrammatical cross-sectional view of the wiring 34 taken along lineF—F in FIG. 5, and FIG. 6(B) is a diagrammatical cross-sectional view ofthe display electrode 32 taken along line G—G in FIG. 5.

Referring to FIG. 5, the hatched regions 72 of display electrode 32 andthe wiring 34 indicate a metal layer such as of aluminum, having a lowelectrical resistance. The region 70 of the display electrode 32indicates a transparent conductive layer such as ITO (Indium Tin Oxide).

Referring to FIGS. 6(A) and 6(B), each of the wiring 34 and the displayelectrode 32 is formed of a laminated structure of the transparentconductive layer 70 and the metal layer 72 having an electricalresistance lower than that of the transparent conductive layer 70. Inthe display electrode 32, the transparent conductive layer 70 extends toits full width, while the metal layer 72 runs along one edge portion ofthe transparent conductive layer 70 and is much narrower in width thanthe transparent conductive layer 70.

On the other hand, both the transparent conductive layer 70 and themetal layer 72 are coextensive in width with the wiring 34, and havethus substantially the same width. In this way, the electricalresistance of the wiring 34 having a width thereacross substantiallynarrower than that of the display electrode 32 is made substantiallysmall. The wirings 36 formed on the second panel substrate 30, althoughnot shown, have a construction similar to that of the wiring 34 shown inFIG. 6(A). In other words, the transparent conductive layer 70 and themetal layer 72 are laminated in substantially the same width.

The wirings 24 and the display electrodes 22 formed on the first panelsubstrate 20 shown in FIG. 3, opposed to the second panel substrate 30shown in FIG. 4, may have a laminated structure of the transparentconductive layer 70 fabricated of ITO and the metal layer 72 fabricatedof aluminum in the same way as in the wirings 34 and the displayelectrodes 32 shown in FIG. 5 and FIGS. 6(A) and 6(B).

In the display device substrate formed of the first panel substrate 20and the second panel substrate 30 in this embodiment as discussed above,each of the wiring 24 shown in FIG. 3 and the wirings 34 and 36 shown inFIG. 4 has the laminated structure of the transparent conductive layer70 and the metal layer 72. Compared with the case in which the wirings24, 34, and 36 are formed only by the transparent conductive layer 70only, the electrical resistance of the wirings 24, 34, and 36 is low.The liquid-crystal display device 10 employing the panel substrates 20and 30 in this embodiment suffers less from an image quality degradationattributed to a voltage drop through the wirings 24, 34, and 36.

Since there is no need for thickening the transparent conductive layer70 for the purpose of reducing the electrical resistance of the displayelectrodes 22 and 23, the light transmittance ratio of the displayelectrodes 22 and 23 is increased. Although the transparent conductivelayer 70 has a full width in the electrodes 22 and 23, the metal layer72 is substantially narrower than the width of the transparentconductive layer 70. The electrical resistance of the display electrodes22 and 32 is thus reduced without any substantial drop in the brightnesslevel of the display caused by the presence of the metal layer 72.

Since the length of each wiring 24 is short in the first panel substrate20 shown in FIG. 3, the wirings 24 and the display electrodes 22 may bemanufactured of the conductive transparent ITO layer 70 only. Because oftheir short lengths, the wirings 36 shown in FIG. 4 may also bemanufactured of the conductive transparent ITO layer 70 only.

Referring to FIG. 3, the transparent conductive layer 70 forming thedisplay electrodes 22 is typically concurrently produced together withthe transparent conductive layer 70 forming the wirings 24. Referring toFIG. 4, the transparent conductive layer 70 forming the displayelectrodes 32 is typically concurrently produced with the transparentconductive layer 70 forming the wirings 34 and the wirings 36. Becauseof their bilayer structure of the transparent conductive layer 70 andthe metal layer 72 in this embodiment, the wirings 24, 34, and 36require no thin design in the transparent conductive layer 70 for asmaller electrical resistance. The transparent conductive layer 70 ofthe display electrodes 22, which is concurrently produced with thetransparent conductive layer 70 of the wirings 24, does not need toomuch thickness. The display electrodes 32, which are concurrentlyproduced with the transparent conductive layer 70 of the wirings 34 andwirings 36, do not need too much thickness. The light transmittanceratio of the display electrodes 22 shown in FIG. 3 and the displayelectrodes 32 shown in FIG. 4 can be higher compared with the case inwhich the electrical resistance of the wirings 24, 34, and 36 is reducedonly by thickening the transparent conductive layer 70.

In the liquid-crystal device substrate of this embodiment, thetransparent conductive layer 70 used in the display electrodes 22 andthe wiring 24 shown in FIG. 3 is thin, compared with the case in whichthe electrical resistance of the transparent conductive layer 70 used inthe wirings 24 shown in FIG. 3 and the wirings 34 and 36 shown in FIG. 4is reduced only by thickening the transparent conductive layer 70.Further, the transparent conductive layer 70 used in the displayelectrodes 32 and the wirings 34 and 36 shown in FIG. 4 is thinned. Forthis reason, the time required to produce the panel substrates 20 and 30is shortened accordingly.

The manufacturing method for manufacturing the first panel substrate 20shown in FIG. 3 and the second panel substrate 30 shown in FIG. 4 is nowdiscussed, referring to the embodiments.

The display electrodes and the wirings in the first panel substrate 20and the second panel substrate 30, produced by laminating thetransparent conductive layer and the metal layer, are manufacturedthrough an transparent conductive layer fabrication step, a metal layerformation step, a first photoresist film formation step, a first etchingstep, a second photoresist film formation step, and a second etchingstep.

FIGS. 7(A)-7(E) are diagrammatic cross-sectional views illustrating themanufacturing process of the second panel substrate 30. FIG. 7(A)illustrates the transparent conductive layer fabrication step and themetal layer formation step, FIG. 7(B) illustrates the first photoresistfilm formation step, FIG. 7(C) illustrates the first etching step, FIG.7(D) illustrates the second photoresist film formation step, and FIG.7(E) illustrates the second etching step. FIGS. 7(A)-7(E) show themanufacturing process of the display electrodes 32 on the left portionsthereof, and the manufacturing process of the wirings 34 on the rightportion thereof. Although a single display electrode 32 and a singlewiring 34 are shown here, a number of electrodes 32 and wirings 34 areemployed in practice.

In the transparent conductive layer fabrication step shown in FIG. 7(A),a transparent conductive layer 70, fabricated of an ITO film, isdeposited on the transparent substrate 31 fabricated of a transparentmaterial such as glass. In the metal layer formation step also shown inFIG. 7(A), the metal layer 72 fabricated of aluminum is deposited on thetransparent conductive layer 70.

In the first photoresist film formation step shown in FIG. 7(B), aphotoresist film is applied on the metal layer 72, and is then subjectedto exposure and development processes. A first photoresist film 74,having a predetermined pattern corresponding to the display electrodes32 and the wirings 34, is thus formed.

In the first etching step shown in FIG. 7(C), the transparent conductivelayer 70 and the metal layer 72 are simultaneously etched using thefirst photoresist film 74, thereby forming the pattern of the displayelectrodes 32 and the wirings 34 in a plan view.

In the second photoresist film formation step shown in FIG. 7(D), thefirst photoresist film 74 remaining on the metal layer 72 in theformation region of the display electrodes 32 is then subjected toexposure and development processes. A second photoresist film 76 havinga predetermined pattern is formed by removing the photoresistcorresponding to the formation area of the transparent conductive layer70. The photoresist remains in the formation area of the wirings 34during the formation of the second photoresist film 76.

In the second etching step shown in FIG. 7(E), the second photoresistfilm 76 is used to partly etch the metal layer 72 corresponding to thedisplay electrodes 32 for patterning. The second etching step isperformed at an etch rate different from that of the first etching stepso that the metal layer 72 is partly etched with the transparentconductive layer 70 almost unetched.

Finally, the second photoresist film 76 is removed through an ashingprocess, for example. The wiring 34 shown in FIG. 6(A) and the displayelectrode 32 shown in FIG. 6(B) thus result.

In accordance with the manufacturing method of the panel substrate ofthis embodiment, the second photoresist film 76 is formed by subjectingagain, to the exposure and development processes, the first photoresistfilm 74 having the predetermined pattern used in the first etching stepshown in FIG. 7(C). Using the second photoresist film 76, the metallayer 72 is partly etched with the part thereof becoming the displayelectrode 32 left through the second etching step shown in FIG. 7(D).The second photoresist film 76 is then removed. The display electrode 32composed of the transparent conductive layer 70 and the narrow metallayer 72 is thus obtained.

In the above-referenced steps, a cycle of application and subsequentremoval of the photoresist film performed one time only result in thedisplay electrode 32 having the narrow metal layer 72. This process thussubstantially reduces the number of steps, compared with the case inwhich the transparent conductive layer 70 and the metal layer 72 areseparately patterned requiring two cycles of application and subsequentremoval steps of the photoresist.

In the manufacturing method of the panel substrate of this embodiment,the transparent conductive layer 70 and the metal layer 72 arelaminated, and are patterned through one cycle of etching to produce thewiring 34.

The manufacturing method of the panel substrate of the present inventionhas been discussed in conjunction with the display electrodes 32 and thewirings 34 in the second panel substrate 30. The wirings 36 are alsomanufactured of the laminated structure of the transparent conductivelayer and the metal layer at the same process steps as that for thewirings 34. The display electrodes 22 and the wirings 24 on the firstpanel substrate 20 shown in FIG. 3 are manufactured in the samemanufacturing method as that for the second panel substrate 30, althoughthe patterns of the display electrodes and the wirings are differentfrom those of the counter parts of the second panel substrate 30.

In this embodiment, the metal layer 72 forming the display electrode 32is arranged on the edge portion of the transparent conductive layer 70as shown in FIG. 6(B). If no problem arises in the light transmittanceratio of the display electrodes, it is not necessary to locate the metallayer 72 along the edge of the transparent conductive layer 70. Forexample, the metal layer 72 may be arranged along the center line of thetransparent conductive layer 70.

In the first embodiment, the liquid-crystal display device is formed ofthe transmissive-type panel substrate, i.e., the display devicesubstrate. In contrast, a second embodiment employs a panel substratehaving a metal layer with slits formed thereon, instead of one of thetwo panel substrates, such as the second panel substrate 30. Theremaining construction of the second embodiment remains unchanged fromthat of the first embodiment. The discussion thereof is thus notrepeated. As shown, like components are identified with like referencenumerals.

FIG. 9 is a plan view diagrammatically showing a second panel substrate80 used in the second embodiment, and corresponds to FIG. 5 illustratingthe first embodiment. FIG. 10 is a cross-sectional view taken along lineG—G in FIG. 9, and corresponds to FIG. 6(B) in conjunction with thefirst embodiment. In this embodiment, the second panel substrate 80replaces the second panel substrate 30 of the first embodiment, therebyproducing a transflective-type liquid-crystal display device.

In the second panel substrate 80, a display electrode 82 is formed of abilayer structure of a transparent conductive layer 70 and a metal layer72. A plurality of slits 84 as apertures are formed in the metal layer72. The metal layer 72 is made of a highly reflective material such asaluminum, copper, silver, or gold. When the slits 84 are arranged in themetal layer 72, the display electrode 82 still has the transparentconductive layer 70 in the slits 84. Regardless of the size of the slits84, an appropriate electric field is applied in the liquid crystal evenin the area of the slits 84.

During a transmissive mode, the transflective-type liquid-crystal deviceallows illumination light rays to be transmitted through the secondpanel substrate 80 through the slits 84 opened in the metal layer 72from behind the second panel substrate 80 and to enter the liquidcrystal 18. During a reflective mode, the liquid-crystal device allowslight rays to transmit the first panel substrate 20, opposed to thesecond panel substrate 80, and then the liquid crystal 18, and to bereflected from the surface of the metal layer 72.

Regardless of the transmissive mode or the reflective mode in thisembodiment, a voltage is applied to the liquid crystal 18 through themetal layer 72 if the slits 84 are small. When large slits 84 are used,the liquid crystal 18 is driven by the transparent conductive layer 70in the slits 84, rather than by the metal layer 72.

The liquid-crystal device 10 having the second panel substrate 80 ofthis embodiment suffers less from an image quality degradationattributed to a voltage drop through the wirings 34 and the displayelectrodes 82. The wirings 34 and the display electrodes 82 of a bilayerstructure of the transparent conductive layer 70 and the metal layer 72eliminates the need for thickening the transparent conductive layer 70for the purpose of a small electrical resistance of the wirings 34.There is no need for thickening too much the transparent conductivelayer 70 in the display electrode 82, which is typically producedconcurrently with the transparent conductive layer 70 of the wirings 34.The light transmittance ratio of the display electrode 82 is thusincreased.

Since the transparent conductive layer 70 is made thin in this way, thetime required to manufacture the second panel substrate 80 is shortened.

In a way similar to the manufacturing method shown in FIGS. 7(A)-7(E),the display electrode 82 of this embodiment is manufactured through atransparent conductive layer fabrication step, a metal layer formationstep, a first photoresist film formation step, a first etching step, asecond photoresist film formation step, and a second etching step. Afterconcurrently etching the transparent conductive layer 70 and the metallayer 72 through the first photoresist film 74, the first photoresistfilm 74 is again subjected to exposure and development processes. Thesecond photoresist film 76 is patterned to etch the metal layer 72 toform the slits 84.

The above-referenced embodiments have been discussed in conjunction withthe passive-matrix liquid-crystal display device. Alternatively, thepresent invention may be applied to an active-matrix liquid-crystaldevice using a two-terminal switching element such as a TFD. Theactive-matrix liquid-crystal panel is manufactured of a pair ofsubstrates, i.e., an element substrate and a counter substrate, and aTN-type liquid crystal encapsulated therebetween.

The element substrate includes a plurality of wirings arranged instripes, TFD arranged for each pixel along each wiring, and a pixelelectrode formed of a transparent conductive layer connected to the TFD.The counter substrate opposed to the element substrate includes widedisplay electrodes running in stripes and intersecting the pixelelectrodes on the element substrate in a plan view.

The element substrate and the counter substrate are assembled with thepixel electrodes on the element substrate being opposed to the displayelectrodes on the counter substrate. A liquid crystal is encapsulatedbetween the two substrates. In this liquid-crystal device, one of thewiring on the element substrate and the display electrode on the countersubstrate works as a scanning electrode, and the other of the wiring andthe display electrode works as a signal electrode.

In the active-matrix TFD liquid-crystal device thus constructed, thewirings formed on the display substrate as the counter substrate areproduced of the laminated structure of the transparent conductive layerand the metal layer in accordance with the present invention. Theliquid-crystal device thus provides the same advantages as those of thepreceding embodiments.

The active-matrix TFD liquid-crystal device is now discussed, referringto FIG. 12.

FIG. 12 shows a major portion of the active-matrix TFD liquid-crystaldevice employing the display device substrate of the present invention,particularly, several pixels of the device in enlargement. The generalconstruction of the liquid-crystal device 1 is shown in FIG. 15. Theliquid-crystal device 1, employing a TFD (Thin Film Diode) as atwo-terminal active element, is a transflective-type liquid-crystaldevice that selectively uses a reflective display working from naturalambient light and a transmissive display based on an illuminatingdevice. The liquid-crystal device 1 adopts the COG (Chip On Glass)technology which permits liquid-crystal drive ICs to be directly mountedon a substrate.

Referring to FIG. 15, the liquid-crystal device 1 is constructed bygluing a first panel substrate 2 a to a second panel substrate 2 b witha sealing member 3 interposed therebetween. A gap, i.e., a cell gap,surrounded by the sealing member 3 between the first panel substrate 2 aand the second panel substrate 2 b, is filled with a liquid crystal.Liquid-crystal drive ICs 4 a and 4 b are directly mounted on the surfaceof an overextension 38 of the first panel substrate 2 a, outwardlyextending over from the second panel substrate 2 b. The second panelsubstrate 2 b is an element substrate on which the TFDs are formed. Thefirst panel substrate 2 a is a counter substrate that is opposed to thesecond panel substrate 2 b.

Arranged on the second panel substrate 2 b in an enclosure surrounded bythe sealing member 3 are a plurality of pixel electrodes which runs inthe direction of rows XX and in the direction of columns YY in a dotmatrix arrangement. Arranged on the first panel substrate 2 a in anenclosure surrounded by the sealing member 3 are striped electrodes. Thestriped electrodes are opposed to the plurality of pixel electrodes onthe second panel substrate 2 b.

A portion of the liquid crystal interposed between the striped electrodeon the first panel substrate 2 a and the pixel electrode on the secondpanel substrate 2 b constitutes a single pixel. A plurality of pixels inthe enclosure surrounded by the sealing member 3 is placed in a dotmatrix arrangement, thereby forming a display area V. The liquid-crystaldrive ICs 4 a and 4 b selectively feed scanning signals and data signalsbetween opposed electrodes of the plurality of pixels, therebycontrolling the alignment of the liquid crystal on a pixel by pixelbasis. Light rays passing the liquid crystal is modulated by thealignment control of the liquid crystal, displaying characters andnumerals on the display area V.

FIG. 12 shows, in enlargement, several of the plurality of pixelsconstituting the display area V in the liquid-crystal device 1. FIG. 13is a cross-sectional view of a single pixel.

Referring to FIG. 12, the first panel substrate 2 a includes a substrate6 a fabricated of glass or plastics, a light reflector 61 formed on theinterior surface of the substrate 6 a, a color filter 62 formed on thelight reflector 61, and transparent striped display electrodes 63 formedon the color filter 62. As shown in FIG. 13, an alignment layer 71 a isformed on the display electrodes 63. The alignment layer 71 a issubjected to a rubbing process as one of the orientation processes. Thedisplay electrodes 63 are fabricated of an conductive transparentmaterial such as ITO (Indium Tin Oxide).

The second panel substrate 2 b opposed to the first panel substrate 2 aincludes a substrate 6 b fabricated of glass or plastics, TFDs (ThinFilm Diodes) 67 formed on the interior surface of the substrate 6 b asan active element functioning as a switching device, and pixelelectrodes 69 respectively connected to the TFDs 67. An alignment layer71 b is formed on the TFDs 67 and the pixel electrodes 69 as shown inFIG. 13. The alignment layer 71 b is subjected to a rubbing process. Thepixel electrodes 69 are fabricated of an conductive transparent materialsuch as ITO (Indium Tin Oxide).

The color filter 62 of the first panel substrate 2 a has color elements62 a of R (red), G (Green), and B (Blue), or C (Cyan), M (Magenta), andY (Yellow) in locations facing the pixel electrodes 69 of the secondpanel substrate 2 b, while having a black mask 62 b in locations notfacing the pixel electrodes 69.

Referring to FIG. 13, the gap, i.e., the cell gap between the firstpanel substrate 2 a and the second panel substrate 2 b is kept to aconstant dimension by spherical spacers 54 dispersed on one of thesubstrates. The liquid crystal L is then encapsulated into the cell gap.

Referring to FIG. 13 and FIG. 14, each TFD 67 includes a first metallayer 65, an insulator 66 formed on the surface of the first metal layer65, and a second metal layer 68 formed on the insulator 66. The TFDs 67have a so-called MIM (Metal Insulator Metal) structure, i.e., thelaminated structure of the first metal layer/insulator/second metallayer.

The first metal layer 65 is fabricated of tantalum only, or atantalum-based alloy. When a tantalum-based alloy is used for the firstmetal layer 65, an element in the group VI to group VIII in the periodictable, such as tungsten, chromium, molybdenum, rhenium, yttrium,lanthanum, or dysprosium, may be added to tantalum as a base material.

The first metal layer 65 is integrally formed with a first layer 79 a ofa line wiring 79. The line wirings 79, running in stripes between thepixel electrodes 69, work as a scanning line for supplying the pixelelectrode 69 with a scanning signal, or as a data line for supplying thepixel electrode 69 with a data signal.

The insulator 66 is fabricated of tantalum oxide (Ta₂O₃) that isobtained by oxidizing the first metal layer 65 through anodizing. Whenthe first metal layer 65 is anodized, the surface of the first layer 79a of the line wiring 79 is also oxidized. Similarly, a second layer 79 bfabricated of tantalum oxide is thus formed.

The second metal layer 68 is fabricated of a conductive material such asCr. The pixel electrode 69 is formed on the substrate 6 b in a mannersuch that the end portion thereof partly overlaps the second metal layer68. An underlying substrate layer of tantalum oxide may be formed on thesurface of the substrate 6 b, before the first metal layer 65 and thefirst layer 79 a of the line wiring 79 are formed. The underlyingsubstrate layer is intended to prevent the first metal layer 65 frompeeling off as a result of a thermal process subsequent to thedeposition of the second metal layer 68, or to prevent an impurity fromdiffusing into the first metal layer 65.

Referring to FIG. 12, a retardation film 52 a is glued onto the exteriorsurface of the substrate 6 a. A polarizer 53 a is glued onto theretardation film 52 a. A retardation film 52 b is glued onto theexterior surface of the substrate 6 b. A polarizer 53 b is glued ontothe retardation film 52 b.

If an STN (Super Twisted Nematic) liquid crystal is used, for example,light passing the liquid crystal may be subject to dispersion, causingdiscoloration to a displayed image. The retardation film 52 a and theretardation film 52 b are optically anisotropic members to eliminate thediscoloration, and may be fabricated of a film that is obtained byuniaxially orienting a resin such as polyvinyl alcohol, polyester,polyether amide, or polyethylene.

The polarizers 53 a and 53 b are optical film elements having thefunction of receiving natural ambient light and outputting a linearlypolarized light ray. The polarizers 53 a and 53 b are produced bysandwiching a polarizer layer between TAC (cellulose triacetate)protective layers. The polarizers 53 a and 53 b are typically arrangedwith the polarization axes thereof different to each other.

The light reflector 61 is fabricated of a light reflective metal such asaluminum. Apertures 49 for transmitting light are formed at locationscorresponding to the pixel electrodes 69 on the second panel substrate 2b, in other words, at locations corresponding to the pixels.

The display electrodes 63 shown in FIG. 12 extend in the YY direction asshown in FIG. 15, forming the wirings 24 and the pads 25 in theoverextension 38 as shown in FIG. 16. The pads 25 are electricallyconnected to the output terminals of the liquid-crystal drive IC 4 bmounted on the overextension 38. The wirings 24 have a bilayer structureformed of the transparent conductive layer 70 and the metal layer 72deposited on the transparent conductive layer 70 as shown in FIG. 6(A).As required, the display electrodes 63 also have a bilayer structure ofthe transparent conductive layer 70 and the narrow-width metal layer 72deposited on the transparent conductive layer 70 as shown in FIG. 6(B).

When the liquid-crystal device 1 thus constructed presents areflective-type display, ambient light entering from the side of aviewer, i.e., from the second panel substrate 2 b into theliquid-crystal display device 1 as shown in FIG. 12, is transmittedthrough the liquid crystal L, reaches the light reflector 61, isreflected therefrom, and returns back into the liquid crystal L. Theorientation of the liquid crystal L is controlled by each pixel by avoltage applied between the pixel electrode 69 and the striped displayelectrode 63, namely, the scanning signal and the data signal. Thereflected light fed to the liquid crystal L is modulated by each pixel,thereby presenting characters and numerals to the viewer.

On the other hand, when the liquid-crystal device 1 presents atransmissive-type display, the illumination device mounted external tothe first panel substrate 2 a, namely, a back light 59 is lit. Lightfrom the back light 59 is transmitted through the polarizer 53 a, theretardation film 52 a, the substrate 6 a, the apertures 49 of the lightreflector 61, the color filter 62, the display electrodes 63, and thealignment layer 71 a, and then reaches the liquid crystal L. Thereafter,the characters and numerals are then presented in the same way as in thereflective-type display.

As discussed above, in this embodiment, the wirings 24 respectivelyconnected to the display electrodes 63 on the first panel substrate 2 ahave a bilayer structure of the transparent conductive layer 70 and themetal layer 72 deposited on the transparent conductive layer 70. Theelectrical resistance of the wirings 24 is thus lower compared with thecase in which of the wirings 24 which are formed of the transparentconductive layer 70 only. The liquid-crystal device 1 thus suffers lessfrom an image quality degradation attributed to a voltage drop throughthe wirings 24.

Since there is no need for thickening the transparent conductive layer70 to reduce the electrical resistance of the wirings 24, thetransparent conductive layer 70 of the display electrodes 63, which istypically produced concurrently with the transparent conductive layer 70of the wirings 24, does not need too much thickness. The lighttransmittance ratio of the display electrodes 63 becomes higher comparedwith the case in which the electrical resistance of the wirings 24 isreduced only by thickening the transparent conductive layer 70.

Since the transparent conductive layer 70 used in the display electrodes63 and the wirings 24 is made thinner compared with the case in whichthe electrical resistance of the wirings 24 is reduced only bythickening the transparent conductive layer 70, the time required toform the counter substrate 2 a, namely, the display device substrate isshortened.

The present invention may be applied to an active-matrix liquid-crystaldevice using a three-terminal switching element such as a thin-filmtransistor (TFT). The active-matrix liquid-crystal panel is manufacturedof a pair of substrates, i.e., an element substrate and a countersubstrate, and a Twisted-Nematic (TN)-type liquid crystal encapsulatedtherebetween.

The element substrate includes scanning lines and data linesintersecting the scanning lines, TFTs, each having the gate thereofconnected to one scanning line and the source thereof connected to onedata line, and conductive transparent pixel electrodes, each connectedto the drain of the TFT. The counter substrate opposed to the elementsubstrate includes wide display electrodes, i.e., common electrodesarranged in stripes and overlapping the horizontally arranged pixelelectrodes on the element substrate.

The liquid-crystal device AC drives the liquid crystal between the pixelelectrode and the display electrode by switching bias voltage levelapplied to the display electrode on a pixel row by pixel row basis,i.e., every horizontal scanning period and every vertical scanningperiod. This drive method is hereinafter referred to as a 1H biasvoltage swing drive method.

In the active-matrix TFT liquid-crystal device of the fourth embodiment,the wirings on the display device substrate, namely, the countersubstrate, are formed by a laminated structure of a transparentconductive layer and a metal layer. The fourth embodiment thus providesthe same advantage as that of the preceding embodiments.

The active-matrix TFT liquid-crystal device is now discussed referringto FIG. 17.

FIG. 17 shows a circuit arrangement of the liquid-crystal device of thefourth embodiment. Arranged in an active matrix area 110 is a matrix ofN rows by M columns of pixel TFTs 108. There are also arranged Nscanning lines respectively connected to the gate electrodes of thepixel TFTs and M signal lines (=m×n) respectively connected to thesources of the pixel TFTs. Respectively connected to the M signal linesare analog switch TFTs (20-11, 20-12, . . . , 20-nm).

The analog switch TFTs are grouped into n blocks, each block including madjacent analog switch TFTs. Analog switch TFTs (20-11, 20-12, . . . ,20-1 m) constitute a first block, analog switch TFTs (20-21, 20-22, . .. , 20-2 m) constitute a second block, . . . , and analog switch TFTs(20-1 n, 20-n2, . . . , 20-nm) constitute an n-th block. The gates ofthe adjacent analog switches (20-11, 20-12, . . . , 20-1 m) in the sameblock are connected together by a first wiring 22-1. The gates of theanalog switch TFTs (20-21, 20-22, . . . , 20-2 m) are connected togetherby a first wiring 22-2, . . . , and the gates of the analog switch TFTs(20-n1, 20-n2, . . . , 20-nm) are connected together by a first wiring22-n.

The sources of analog switch TFTs (20-11, 20-21, . . . , 20-n1), whichare included different blocks and are not adjacent to each other, areconnected together by a second wiring 24-1. Similarly, the sources ofthe analog switch TFTs (20-12, 20-22, . . . , 20-n2) are connectedtogether by a second wiring 24-2, . . . , and the sources of the analogswitch TFTs (20-1 m, 20-2 m, . . . , 20-nm) are connected together by asecond wiring 24-m.

The analog switch TFTs are divided into n blocks, each block including mTFTs. By controlling the analog switch TFTs in each block by a controlsignal for on and off switching, the number of signal line terminals isreduced to 1/n. For example, M signal line terminals, if no analogswitches are employed, are reduced to m signal line terminals (=M/n). Adata driver is connected to m lines of the second wiring 24-1 through24-m. This arrangement reduces the number of data drivers and the numberof terminals, thereby miniaturizing the device and reducing the cost ofthe device.

In the liquid-crystal device of this embodiment, the amplitude of theinput signal supplied to the sources of the analog switch TFTs 20-11, .. . , 20-nm through the second wirings 24-1, . . . , 24-m is preferably5 V or lower. This arrangement reduces the amount of shift in thethreshold voltage of the analog switch TFT, thereby assuring thereliability of the device and increasing image quality.

FIG. 22 plots measurement results of the shift in the threshold voltageof the analog switch TFT and operating time. The gate voltage Vg is 20V, and the load capacitance C of the liquid crystal is set to be atypical load capacitance in a standard liquid crystal panel, namely, ashigh as 10 pF. The operating frequency f is set to be 230 kHz.

The liquid-crystal device of this embodiment divides the analog switchTFTs into the n blocks, thereby reducing the number of the data driversand the number of the terminals. For example, the number of the analogswitch TFTs is reduced to 1/n, and the time permitted to charge thepixel electrode is shorter than normal. For this reason, the operatingfrequency f is set to be higher. Shift characteristics of the thresholdvalue of the TFT in response to a rectangular-wave input signal havingan amplitude of 10 V (Vd=10 V) are represented by curve “G”, and shiftcharacteristics in response to a rectangular-wave input signal having anamplitude of 5 V (Vd=5 V) are represented by “H”.

The threshold voltage of the analog switch TFT is shifted by 1 V withinan operating time of 200 hours in response to an input signal amplitudeof 10 V. When the input signal has an amplitude of 5 V, the shift amountof the threshold voltage is maintained within 1 V for an operating timeof 10000 hours.

When the shift amount in the threshold voltage becomes larger than 1 V,an amount of charge written to each electrode pixel in response to datais insufficient. Specifically, the pixel electrode cannot be maintainedat a desired voltage, and the contrast of the display is degraded. Forexample, when the threshold voltage shifts toward the negative side by 1V with the threshold voltage of the analog switch TFT at 1 V or so, theanalog switch TFT is put into a depletion mode. Even with the analogswitch TFT in an off state, current is leaked, thereby leading to adegradation in display characteristics.

To increase the reliability of the liquid-crystal device, the shiftamount of the threshold voltage must be maintained to within 1 V withinat least an operating time of 1000 hours. Preferably, the shift amountof the threshold voltage is maintained to within 1 V for severalthousand hours. With Vd=10 V, the shift amount becomes larger than 1 Vwithin an operating time of 200 hours, and reaches 2 V within anoperating time of 1000 hours as shown in FIG. 22. This is detrimental toassuring the reliability of the device. Using the input signal with theamplitude thereof not higher than 5 V, the liquid-crystal device of thisembodiment alleviates concentration of electric field at the end portionof the source of the analog switch TFT. In this way, the shift amount ofthe threshold voltage is kept to within 1 V for an operating time of10000 hours or so, and the reliability of the device is assured with asufficient safety margin allowed. Further with the amplitude of theinput signal not higher than 5 V, the difference between penetrationvoltages of the analog switch TFTs is reduced. The direct-currentvoltage applied to the liquid crystal is lowered.

Referring to FIG. 22, the gate voltage of the analog switch TFT is setto be 20 V in the case Vd=5 V to assure proper comparison with the caseof Vd=10 V. When the amplitude of the input signal is 5 V, namely, Vd=5V, writing performance is as good as when the gate voltage Vg is 20 Vwith Vd=10 V. In this case, the shift amount of the threshold voltage isreduced to be lower than curve “H” shown in FIG. 22, and the reliabilityof the device is further improved. To further improve the reliability,the input voltage is preferably not higher than 3 V. Curve “I” shown inFIG. 22 represents shift characteristics in response to the inputvoltage of 5 V at an operating frequency of 32 kHz.

In the liquid-crystal device of this embodiment, the pixel TFT and theanalog switch TFT, fabricated of polycrystalline silicon ormonocrystalline silicon, are integrally formed on a glass substrate.Display characteristics will be degraded if charging and discharging ofa pixel electrode are not completed within a predetermined duration oftime when an input signal is applied to an analog switch TFT. For thisreason, the on resistance of the analog switch TFT needs to be reduced.When the analog switch TFTs are divided into the n blocks to reduce thenumber of the data drivers, the requirement for the reduction of the onresistance is even more rigorous. Amorphous silicon TFTs have anextremely low mobility. For their on resistance characteristics, theamorphous silicon TFTs cannot be used for an analog switch TFT even ifit can be used for a pixel TFT.

In this embodiment, the pixel TFT and the analog switch TFT arefabricated of polycristal silicon or monocrystal silicon, having amobility substantially higher than that of the amorphous silicon TFT.This arrangement allows the pixel TFT and the analog switch TFT to beintegrally formed on the glass substrate. With the pixel TFT and theanalog switch TFT integrally formed on the glass substrate, externaldimensions of the liquid-crystal device are miniaturized and the costthereof is reduced.

FIG. 18 illustrates the manufacturing method for integrally forming thepixel TFT and the analog switch TFT and the structure of the TFTs. Anunderlying insulator 132 for preventing impurities from diffusing from aglass substrate 130 is deposited on the glass substrate 130. Apolycrystalline silicon thin layer 134 is then deposited on theunderlying insulator 132. The crystallinity of the polycrystallinesilicon thin layer 134 must be improved to increase mobility in responseto the field effect. To this end, the polycrystalline silicon thin filmis recrystallized using a laser anneal or solid phase epitaxy, orpolycrystalline silicon resulting from recrystallizing an amorphoussilicon film is used. The polycrystalline silicon thin layer 134 ispatterned in islands, and a gate insulator 136 is then depositedthereon.

A gate electrode 138 is formed of a metal, for example. The doping withan impurity such as phosphorus ions is performed over the entire surfaceof the laminate. An interlayer insulator (SiO₂) 140 is then formed. Ametal thin layer 142, of aluminum (Al) for example, is deposited forsignal lines. A pixel electrode 144 is fabricated of a transparentconductive layer such as of ITO. A passivation layer 146 is then formed.A substrate having the pixel TFT integrated with the analog switch TFTthus results. The substrate is then subjected to an alignment process. Acounter substrate 135, which has been similarly subjected to analignment process, is arranged to be opposed the element substrate witha gap of several μm maintained therebetween. The liquid crystal L isthen encapsulated between the substrates. A liquid-crystal device isthus produced.

The counter substrate 135 has a display electrode 22 formed on thesurface facing the liquid crystal L as shown in FIG. 3. Terminals fromexternal circuits are connected to the pads 25 of the wiring 24 to whichthe display electrodes 22 extend. The wirings 24 has a bilayer structureof the transparent conductive layer 70 and the metal layer 72 as shownin FIG. 6(A). As required, the display electrodes 22 also have a bilayerstructure of the wide-width transparent conductive layer 70 and thenarrow-width metal layer 72 deposited on the transparent conductivelayer 70 as shown in FIG. 6(B).

The liquid-crystal device 101 shown in FIG. 17 may be designed in anexternal configuration shown in FIG. 19, for example. Referring to FIG.19, a display area, i.e., an active matrix area 160, is shown enclosedby a broken line. The liquid crystal material is interposed between acolor filter substrate 162 and a TFT substrate 164. The analog switchTFTs and their associated wirings are arranged on an area 166.

A data driver 170 is mounted using a TAB (Tape Automated Bonding) tape168. A data driver 172 and a scanning driver 174 are similarly mountedusing the TAB tape 168.

A circuit board 176 bears wirings and capacitors for feeding signals tothe data drivers 170, and 172, and the scanning driver 174. As required,a control circuit for controlling the data drivers and the scanningdriver is arranged on the circuit board 176.

In the embodiment shown in FIG. 19, half of the analog switch TFTs ismounted on the top side of the active matrix area 160, while the otherhalf of the analog switch TFTs is mounted on the underside of the activematrix area 160. The M signal lines shown in FIG. 17 are thusinterdigitally arranged from the top side and the bottom side of theactive matrix area 160. The data drivers and the scanning driver aremounted on the same sides of the color filter substrate 162 and the TFTsubstrate 164 forming a liquid-crystal panel. In this way, the dimensionL3 of the liquid-crystal device of this embodiment is substantiallyreduced. The liquid-crystal device suitably finds applications in mobiletelephones, mobile electronic terminals, etc.

As discussed above, the amplitude of the input signal to the source ofthe analog switch TFT is preferably not higher than 5 V to properlycontrol the shift amount of the threshold voltage of the analog switchTFT in the liquid-crystal device 101 of this embodiment. However, thefollowing problem can arise in the standard drive method.

FIG. 21 shows the standard drive method using a field polarity reversal.Since the liquid crystal needs to be driven from an alternating current,a signal Vs applied to the signal line is reversed with respect to apredetermined voltage Vc in polarity every predetermined period.Referring to FIG. 21, the voltage Vs swings in a large amplitude. Sincea standard TN liquid crystal needs a voltage of ±5 V, the voltage Vs hasan amplitude of 10 V or so. A voltage Vcom applied to the counterelectrode is lower than the central voltage Vc of the voltage Vs by ΔVto compensate for a penetration voltage that occurs when the pixel TFTis in an off state. Here, the condition of average ΔV=Vc−Vcom holds.

Referring to a drive voltage waveform diagram shown in FIG. 21, theamplitude of the input signal to the analog switch TFT needs to be aslarge as 10 V. The amplitude of the input signal to the analog switchTFT also needs to be large. For this reason, the input signal cannot bereduced to an amplitude smaller than 5 V. Accordingly, the presentembodiment reverses the polarity of the voltage applied to the counterelectrode relative to the input signal every horizontal scanning periodas shown in FIG. 20. (This drive method is called a 1H bias voltageswing drive method.)

Referring to FIG. 21, the polarity of the voltage Vs is reversed withrespect to the voltage Vc every field. In the 1H bias voltage swingdrive method, the polarity of the Vcom is reversed every horizontalscanning period. This eliminates the need for the polarity reversal ofthe voltage Vs. The amplitude of the Vs is thus reduced. For thisreason, the input signal to the analog switch TFT can be set to besmaller than 5 V while the display quality of the device is maintained.Since the operating voltage of the data drivers is lowered, the devicecan be manufactured on a manufacturing process supporting 5 V withstandvoltage specifications. The data drivers are thus miniaturized, andreduced in power consumption and costs.

The 1H bias voltage swing drive method satisfies both the reliabilityrequirement to the analog switch TFT and low operating voltagerequirement of the data drivers. Referring to FIG. 20, the condition ofaverage ΔV=average Vs−average Vcom holds to control the adverse effectof penetration voltage.

In this embodiment, as discussed above, the striped display electrodes22 shown in FIG. 3 are formed on the counter substrate 135 shown in FIG.18. The wirings 24 leading to the display electrodes 22 have a laminatedstructure of the transparent conductive layer 70 and the metal layer 72as shown in FIG. 6(A). The electrical resistance of the wiring 24 isreduced to be lower than when the wirings 24 are fabricated of thetransparent conductive layer 70 only. The liquid-crystal device thussuffers less from an image quality degradation attributed to a voltagedrop through the wirings 24.

Since there is no need for thickening the transparent conductive layer70 to reduce the electrical resistance of the wirings 24, thetransparent conductive layer 70 of the display electrodes 63, which istypically produced concurrently with the transparent conductive layer 70of the wirings 24, does not need too much thickness. The lighttransmittance ratio of the display electrodes 63 becomes higher comparedwith the case in which the electrical resistance of the wirings 24 isreduced only by thickening the transparent conductive layer 70.

Since the transparent conductive layer 70 used in the display electrodes63 and the wirings 24 is made thinner compared with the case in whichthe electrical resistance of the wirings 24 is reduced only bythickening the transparent conductive layer 70, the time required toform the counter substrate 2 a, namely, the display device substrate isshortened.

FIGS. 8(A), 8(B), and 8(C) show embodiments of electronic equipmentwhich incorporates one of the liquid-crystal device 10 shown in FIG. 1,the liquid-crystal device 1 shown in FIG. 15, and the liquid-crystaldisplay device 101 shown in FIG. 17. FIG. 8(A) shows a mobile telephone88 having the liquid-crystal device 10 or the like on the upper portionthereof. FIG. 8(B) shows a wristwatch 92 having the liquid-crystaldevice 10 or the like as a display section thereof. FIG. 8(C) shows amobile information terminal 96 having the liquid-crystal device 10 orthe like as the display section thereof and an input section 98.

Besides the liquid-crystal device 10, each of the above electronicequipment includes a diversity of circuits including a displayinformation output source 86, a display information processor 87, aclock generator 89, etc., and a display signal generator 93 including apower source circuit 91 for supplying these circuits with power. Themobile information terminal 96 shown in FIG. 8(C) displays, on thedisplay section thereof, an image generated in response to the supply ofdisplay signals produced by the display signal generator 93 based oninput information from the input section 98.

The electronic equipment incorporating one of the liquid-crystal devices10 and the like of the above embodiments is not limited to the mobiletelephone, the wristwatch, and the mobile information terminal. Theelectronic equipment may include a notebook computer, an electronicnotebook, a pager, a tabletop calculator, a POS terminal, an IC card, amini-disc player, etc.

The preferred embodiments of the present invention have been discussed.The present invention is not limited to these embodiments. A variety ofchanges and modifications of these embodiments is possible within thescope of the appended claims.

In the above embodiments, the transparent conductive layer is fabricatedof ITO, and the metal layer is fabricated of aluminum. As long as amaterial forming the transparent conductive layer has a sufficientlyhigh light transmittance and a sufficient conductivity, any material isacceptable. For example, tin oxide or silver may be employed. Thetransparent conductive layer may be a transflective layer partlyreflective and partly transmissive. As long as a material forming themetal layer has a sufficient conductivity, any material is acceptable.For example, chromium, copper, silver, or gold may be acceptable.

The liquid-crystal panel discussed above may include a color filter onthe interior surface of one of the substrates, thereby making a colordisplay device. The color filter is preferably formed beneath thedisplay electrode.

In each of the above embodiments, an STN liquid crystal is used for theliquid-crystal panel. The liquid-crystal panel is not limited to this.Employed is any of a variety of liquid-crystal panels of TN (TwistedNematic) type, guest-host type, phase transition type, bistable TN(Twisted Nematic) type, and ferroelectric type. The display electrode isnot limited to a striped configuration. The display electrode may have acharacter such as an icon.

A transmissive-type liquid-crystal device is shown in the embodiment inFIG. 1. The present invention is applicable to a reflective-type displaydevice. Such a liquid-crystal device employs a reflector behind thesubstrate or a reflective electrode as one of the display electrode,instead of a back light unit.

The present invention is not limited to any of the above embodiments. Avariety of changes, modifications and equivalents are possible withinthe scope of the present invention.

As discussed above, the present invention includes a wiring having alaminated structure of a transparent conductive layer and a metal layer.The electrical resistance of the wiring is lower than when the wiring isconstructed of the transparent conductive layer only. A liquid-crystaldevice incorporating the display device substrate of this inventionsuffers less from image quality degradation attributed to a voltage dropacross the wiring.

Since there is no need for thickening the transparent conductive layerto reduce the electrical resistance of the wirings, the transparentconductive layer of the display electrodes, which is typically producedconcurrently with the transparent conductive layer of the wirings, doesnot need too much thickness. The light transmittance ratio of thedisplay electrodes becomes higher compared with the case in which theelectrical resistance of the wirings is reduced only by thickening thetransparent conductive layer.

Since the transparent conductive layer used in the display electrodesand the wirings is made thinner compared with the case in which theelectrical resistance of the wirings is reduced only by thickening thetransparent conductive layer, the time required to form the countersubstrate, namely, the display device substrate is shortened.

1. A method for manufacturing a display device substrate comprising: atransparent conductive layer fabrication step for fabricating atransparent conductive layer on the display device substrate; a metallayer depositing step for depositing a metal layer on the transparentconductive layer; a first etching step for concurrently etching thetransparent conductive layer and the metal layer using a firstphotoresist film; and a second etching step for etching only the metallayer using a second photoresist film, wherein the second photoresistfilm having a predetermined pattern is created by subjecting the firstphotoresist film to exposure and development processes.
 2. The methodaccording to claim 1, wherein the metal layer in the display electrodeis etched through the second etching step so that the metal layer isleft on only the edge portion of the transparent conductive layer. 3.The method according to claim 1, wherein the metal layer in the displayelectrode is etched through the second etching step so that the metallayer has an aperture on the transparent conductive layer.
 4. Amanufacturing method for manufacturing a display device including adisplay electrode and wiring, the manufacturing method comprising:fabricating a transparent conductive layer on a display devicesubstrate; depositing a metal layer on the transparent conductive layer;concurrently etching the transparent conductive layer and the metallayer; and after concurrently etching the transparent conductive layerand the metal layer, etching only the metal layer at a portion of aregion that corresponds to the display electrode and maintaining themetal layer at a remainder of the region that corresponds to the displayelectrode to provide a reflective function to the display electrode.